Full-color light emitting diode display having improved luminance and method of manufacturing the same

ABSTRACT

A full-color light emitting diode (LED) display having an improved luminance is provided herein. More specifically, provided herein are a full-color LED display, in which an amount of light blocked by electrodes and not extracted is minimized and ultra-small LED devices are connected to ultra-small electrodes without defects such as electrical short circuits and the like, wherein the full-color LED display exhibits a further improved luminance when a direct current (DC) driving voltage is used and each pixel of the full-color LED display exhibits uniform luminance when the DC driving voltage is used, and a method of manufacturing the same.

BACKGROUND Field of the Invention

The present invention relates to a full-color light emitting diode (LED)display, and more particularly, a full-color LED display in which anamount of light blocked by electrodes and not extracted is minimized andultra-small LED devices are connected to ultra-small electrodes withoutdefects such as electrical short circuits and the like, wherein thefull-color LED display exhibits a much improved luminance when a directcurrent (DC) driving voltage is used, and each pixel of the full-colorLED display exhibits uniform luminance when the DC driving voltage isused, and a method of manufacturing the same.

Discussion of Related Art

Light emitting diode (LED) devices have been actively developed sinceNakamura of Nichia Co. in Japan succeeded in fusing a high-qualitysingle crystalline GaN nitride semiconductor in 1992 by applying alow-temperature GaN compound buffer layer thereto. An LED is asemiconductor having a structure, in which an N-type semiconductorcrystal having electrons as a plurality of carriers and a P-typesemiconductor crystal having holes as a plurality of carriers are joinedto each other using characteristics of a compound semiconductor, and isa semiconductor device which converts electric signals into light havinga desired wavelength band to display the light. In relation to such anLED, Korean Patent Laid-Open Publication No. 10-2009-0121743 discloses amethod of manufacturing an LED and an LED manufactured thereby.

The LED is a green component which has a very low energy consumption dueto high light conversion efficiency thereof, has a semi-permanentlifetime, and is eco-friendly. LEDs are being applied in many fields,such as traffic lights, mobile phones, vehicle headlights, outdoordisplay boards, liquid crystal display backlight units (LCD BLUs),indoor and outdoor lighting, etc., and are being actively researchdomestically and internationally.

One of the fields where LEDs are recently being widely used is a displayfield. Currently, an LED is a light source provided in a BLU of an LCDdevice, which is one of light receiving type displays, and is beingwidely used only in the display field. A full-color LED display capableof directly displaying an image through LEDs is not commerciallyavailable. Since there are technical limitations in a process ofmounting and arranging LEDs in a panel, it is not easy to commercializefull-color LED displays. Specifically, in order to realizehigh-resolution image quality, a number of pixels are needed, and aplurality of subpixels which implement different colors have to beincluded in a unit pixel. In order for a plurality of pixels to bemounted within a limited unit area, the size of the unit pixel has to bereduced, and the size of the subpixel also has to be reduced. At thistime, a size of an LED included in each subpixel has to also be reduced,and when a plurality of LEDs are provided in a single subpixel, the sizeof the LED has to be further reduced. However, it is not easy to mountminiaturized LEDs at desired positions on an electrode line.Particularly, a process of mounting ultra-small LEDs that cannot bepicked up by people or machines is very difficult. Therefore, it is notpossible to arrange LED devices, which are individually grown and haveindividually sizes in the unit of micro or nanometer, on a displayelectrode line, and thus commercialization of the full-color LED displayhas continuously been delayed.

In order to solve the above problems, the inventor of the presentinvention proposed a disclosure, Korean Patent Registration No. 1209449,in which a coupling linker is attached to one end of an ultra-small LEDdevice and another coupling linker capable of coupling with the couplinglinker is attached to an electrode, on which the ultra-small LED deviceis mounted, to realize a full-color LED display. However, mountingactual miniature LED devices on an electrode with only coupling linkersis difficult, and particularly, mounting of ultra-small LED devicesupright between electrode lines vertically disposed is very difficult.Even when an LED display is manufactured, the number of LED devicesinterposed to be upright between electrodes vertically disposed issignificantly low, and thus only an LED display having very lowluminance is manufactured.

Accordingly, the present inventor proposed a disclosure, Korean PatentRegistration No. 1436123, for implementing an LED display manufacturedby implementing ultra-small LED devices in the unit of nanometer aselectrode assemblies by applying power to an ultra-small electrode line.However, in a display including ultra-small LED electrode assembliesrealized through such a technique, the number of ultra-small LED deviceswhich did not emit light when a direct current (DC) was applied theretoas driving power was remarkably increased, and thus it was difficult toobtain a desired luminance and power selection had limitations, that is,alternating current (AC) power had to be applied to the LED electrodeassemblies as the driving power. This result was due to a characteristicof an LED serving as a rectifier. A direction of a current in a devicecan be determined according to a semiconductor layer structure in thedevice. For example, in the case of an LED in which a P-typesemiconductor and an N-type semiconductor are joined, when positive (+)power is supplied to the P-type semiconductor and negative (−) power issupplied to the N-type semiconductor, a current can flow through the LEDdue to a potential difference generated by free electrons of the N-typesemiconductor moving toward holes of the P-type semiconductor, and adiode can emit light by recombining the free electrons and the holes.However, when negative (−) power is supplied to the P-type semiconductorand positive (+) power is supplied to the N-type semiconductor, thediode cannot emit light because a current does not flow therein.Therefore, a display including ultra-small LED electrode assemblies andembodied such that an orientation tendency between semiconductordirectivity of ultra-small LED devices and different mounting electrodesdoes not exist according to Korean Patent Registration No. 436123 had aproblem in that a luminance thereof is significantly degraded becausesome of the ultra-small LED devices did not emit light when DC drivingpower was used.

Accordingly, there is an urgent need to develop a full-color display inwhich ultra-small LED devices are connected to ultra-small electrodeswithout electrical short circuits, selection of driving power has nolimits, luminance is further improved, and each pixel thereof hasuniform luminance.

SUMMARY OF THE INVENTION

The present invention is directed to providing a full-color lightemitting diode (LED) display including ultra-small LED electrodeassemblies, in which an amount of light blocked by electrodes and notextracted is minimized and ultra-small LED devices are connected toultra-small electrodes without defects such as electrical short circuitsand the like, and a method of manufacturing the same.

In addition, the present invention is directed to providing a full-colorLED display, in which selection of driving power of the full-color LEDdisplay has no limits, and thus a luminance characteristic exhibitedwhen direct current (DC) driving power is used is higher than or equalto that exhibited when alternating current (AC) power is used, and amethod of manufacturing the same.

Further, the present invention is directed to providing a full-color LEDdisplay, in which intensity of light emitted by pixels or subpixels issimilar due to a DC driving voltage, and thus uniform luminancecharacteristics and color reproducibility are exhibited by the entiredisplay, and a method of manufacturing the same.

Furthermore, the present invention is directed to providing a full-colorLED display capable of having excellent color reproducibility due tosignificantly improved intensity of light emitted in a specificwavelength band, and a method of manufacturing the same.

According to an aspect of the present invention, there is provided amethod of manufacturing a full-color LED display having an improvedluminance, including forming subpixels, each of which includes at leastone ultra-small LED electrode assembly configured to emit light havingsubstantially the same light color, wherein a method of manufacturingthe ultra-small LED electrode assembly includes: (1) introducing asolution including ultra-small LED devices to a mounting electrode lineincluding a first mounting electrode and a second mounting electrode,which is formed on the same plane as the first mounting electrode andspaced apart from the first mounting electrode; and (2) self-mountingthe ultra-small LED devices by applying power, which has an asymmetricassembly voltage of 10 V or more according to Equation 1, to themounting electrode line such that one end of each of the ultra-small LEDdevices comes into contact with the first mounting electrode and theother end thereof comes into contact with the second mounting electrode.Asymmetric Assembly Voltage (V)=∥A(V)|−|B(V)∥  [Equation 1]

Here, A indicates a magnitude of an upper end of a peak voltage of theapplied power, and B indicates a magnitude of a lower end of the peakvoltage thereof.

The power may have a frequency of 50 kHz to 1 GHz.

An insulating partition wall configured to surround the mountingelectrode line may be formed, and then the ultra-small LED electrodeassembly may be manufactured by introducing the solution including theplurality of ultra-small LED devices to the insulating partition wall.

The method may further include performing a thermal process on theultra-small LED electrode assembly at a temperature of 200 to 1,000° C.for 0.5 to 10 minutes after the self-mounting of the ultra-small LEDdevices is performed.

The method may further include forming an ohmic layer and portions onwhich the first and second mounting electrodes are in contact with endportions of each of the ultra-small LED devices after the self-mountingof the ultra-small LED devices is performed.

The light color may be blue or white or may be the same as that ofultraviolet (UV) light.

The method may further include forming short-wavelength transmissionfilters on the formed subpixels; patterning green color conversionlayers on the short-wavelength transmission filters corresponding tosome subpixels selected among the subpixels, and patterning red colorconversion layers on the short-wavelength transmission filterscorresponding to some subpixels selected among the remaining subpixels;and forming long-wavelength transmission filters on portions includingthe green color conversion layers and the red color conversion layers.

The power may have an asymmetric assembly voltage of 18 V or moreaccording to Equation 1.

The ultra-small LED device may have a length of 100 nm to 10 μm.

The ultra-small LED electrode assembly may further include an insulatingfilm formed on outer surfaces of the first mounting electrode and thesecond mounting electrode and the plurality of ultra-small LED devicesmay come into contact with the first mounting electrode and the secondmounting electrode through the insulating film.

According to still another aspect of the present invention, there isprovided a full-color LED display having an improved luminance,including subpixels, each of which includes at least one ultra-small LEDelectrode assembly configured to emit light having substantially thesame light color, wherein: the ultra-small LED electrode assemblyincludes a mounting electrode line including a first mounting electrodeand a second mounting electrode, which are formed on the same plane andspaced apart from each other, and ultra-small LED devices, which eachhave one end in contact with the first mounting electrode and the otherend in contact with the second mounting electrode; and a luminance gainaccording to Equation 2 is 1.1 or more.

$\begin{matrix}{{{Luminance}\mspace{14mu}{Gain}} = \frac{\begin{matrix}{{Luminance}\mspace{14mu}{of}\mspace{14mu}{ultra}\text{-}{small}\mspace{14mu}{LED}\mspace{14mu}{electrode}} \\{{assembly}\mspace{14mu}{driven}\mspace{14mu}{by}\mspace{14mu}{DC}\mspace{14mu}{voltage}\mspace{14mu}\left( {{cd}\text{/}m^{2}} \right)}\end{matrix}}{\begin{matrix}{{Luminance}\mspace{14mu}{of}\mspace{14mu}{ultra}\text{-}{small}\mspace{14mu}{LED}\mspace{14mu}{electrode}} \\{{assembly}\mspace{14mu}{driven}\mspace{14mu}{by}\mspace{14mu}{AC}\mspace{14mu}{voltage}\mspace{14mu}\left( {{cd}\text{/}m^{2}} \right)}\end{matrix}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

According to yet another aspect of the present invention, there isprovided a full-color LED display having an improved luminance,including subpixels, each of which includes at least one ultra-small LEDelectrode assembly configured to emit light having substantially thesame light color, wherein: the ultra-small LED electrode assemblyincludes a mounting electrode line including a first mounting electrodeand a second mounting electrode, which are formed on the same plane andspaced apart from each other, and ultra-small LED devices including afirst semiconductor layer and a second semiconductor layer, each ofwhich one end is in contact with the first mounting electrode and theother end is in contact with the second mounting electrode; and apercentage of the ultra-small LED devices, of which the firstsemiconductor layer is in direct or indirect contact with the firstmounting electrode, among all of the ultra-small LED devices in contactwith the mounting electrode is 60% or more.

The ultra-small LED device may have an aspect ratio of 1.2 to 100.Further, the ultra-small LED device may have a length of 100 nm to 10μm.

The ultra-small LED device may include a first semiconductor layer, anactive layer formed on the first semiconductor layer, a secondsemiconductor layer formed on the active layer, and an insulating thinfilm configured to cover at least an entire outer surface of the activelayer among outer surfaces of the ultra-small LED device. Here, onesemiconductor layer among the first semiconductor layer and the secondsemiconductor layer may include at least one N-type semiconductor layer,and the other semiconductor layer may include at least one P-typesemiconductor layer.

The ultra-small LED electrode assembly may have a luminance gain of 1.3or more according to Equation 2.

In the ultra-small LED electrode assembly, the number of the mountedultra-small LED devices per unit area (mm²) may be 1,000 or more.

The ultra-small LED electrode assembly may further include an insulatingfilm formed on outer surfaces of the first mounting electrode and thesecond mounting electrode and the plurality of ultra-small LED devicesmay come into contact with the first mounting electrode and the secondmounting electrode through the insulating film.

A percentage of the ultra-small LED devices, of which the firstsemiconductor layer is in contact with the first mounting electrode,among all of the ultra-small LED devices may be 80% or more.

The ultra-small LED electrode assembly may further include an ohmiclayer and portions in which the first and second mounting electrodes arein contact with end portions of each of the ultra-small LED devices.

The light color may be blue or white or may be the same as that ofultraviolet (UV) light.

The full-color LED display may further include short-wavelengthtransmission filters formed on the subpixels; color conversion layersincluding green color conversion layers provided on the short-wavelengthtransmission filters corresponding to some subpixels selected among thesubpixels and red color conversion layers provided on theshort-wavelength transmission filters corresponding to some subpixelsselected among the remaining subpixels; and long-wavelength transmissionfilters provided on the color conversion layers.

According to another aspect of the present invention, there is provideda method of manufacturing a full-color LED display having an improvedluminance, including forming subpixels, each of which includes at leastone ultra-small LED electrode assembly configured to emit light havingsubstantially the same light color, wherein: the light color is dividedinto a different plurality of light color groups including a first lightcolor, a second light color, and a third light color; and a method ofmanufacturing the ultra-small LED electrode assembly includes: (a)introducing a solution including ultra-small LED devices to a mountingelectrode line including a first mounting electrode and a secondmounting electrode, which is formed on the same plane as the firstmounting electrode and spaced apart from the first mounting electrode;and (b) self-mounting the ultra-small LED devices by applying power,which has an asymmetric assembly voltage of 10 V or more according toEquation 1, to the mounting electrode line such that one end of each ofthe ultra-small LED devices comes into contact with the first mountingelectrode and the other end thereof comes into contact with the secondmounting electrode.

The power may have a frequency of 50 kHz to 1 GHz.

An insulating partition wall configured to surround the mountingelectrode line may be formed, and then the ultra-small LED electrodeassembly may be manufactured by introducing the solution including theplurality of ultra-small LED devices to the insulating partition wall.

The method may further include performing a thermal process on theultra-small LED electrode assembly at a temperature of 200 to 1,000° C.for 0.5 to 10 minutes after the self-mounting of the ultra-small LEDdevices is performed.

After the self-mounting of the ultra-small LED devices is performed, themethod may further include forming an ohmic layer and portions on whichthe first and second mounting electrodes are in contact with endportions of each of the ultra-small LED devices.

The power may have an asymmetric assembly voltage of 18 V or moreaccording to Equation 1.

The ultra-small LED device may have a length of 100 nm to 10 μm.

The ultra-small LED electrode assembly may further include an insulatingfilm formed on outer surfaces of the first mounting electrode and thesecond mounting electrode and the plurality of ultra-small LED devicesmay come into contact with the first mounting electrode and the secondmounting electrode through the insulating film.

Among the plurality of light color groups, the first light color may beblue, the second light color may be green, and the third light color maybe red. Here, the plurality of light color groups may further include afourth light color group of which a light color is white.

According to yet another aspect of the present invention, there isprovided a full-color LED display having an improved luminance,including subpixels, each of which includes at least one ultra-small LEDelectrode assembly configured to emit light having substantially thesame light color, wherein: the light color is divided into a pluralityof different light color groups including a first light color, a secondlight color, and a third light color; the ultra-small LED electrodeassembly includes: a mounting electrode line including a first mountingelectrode and a second mounting electrode, which are formed on the sameplane and spaced apart from each other; and ultra-small LED devices,which each have one end in contact with the first mounting electrode andthe other end in contact with the second mounting electrode; and aluminance gain according to the following Equation 2 is 1.1 or more.

$\begin{matrix}{{{Luminance}\mspace{14mu}{Gain}} = \frac{\begin{matrix}{{Luminance}\mspace{14mu}{of}\mspace{14mu}{ultra}\text{-}{small}\mspace{14mu}{LED}\mspace{14mu}{electrode}} \\{{assembly}\mspace{14mu}{driven}\mspace{14mu}{by}\mspace{14mu}{DC}\mspace{14mu}{voltage}\mspace{14mu}\left( {{cd}\text{/}m^{2}} \right)}\end{matrix}}{\begin{matrix}{{Luminance}\mspace{14mu}{of}\mspace{14mu}{ultra}\text{-}{small}\mspace{14mu}{LED}\mspace{14mu}{electrode}} \\{{assembly}\mspace{14mu}{driven}\mspace{14mu}{by}\mspace{14mu}{AC}\mspace{14mu}{voltage}\mspace{14mu}\left( {{cd}\text{/}m^{2}} \right)}\end{matrix}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Here, a magnitude of an applied direct current (DC) voltage V is equalto that of an effective voltage (Vrms) of sine wave alternating current(AC) power.

According to yet another aspect of the present invention, there isprovided a full-color LED display having an improved luminance,including subpixels, each of which includes at least one ultra-small LEDelectrode assembly configured to emit light having substantially thesame light color, wherein: the light color is divided into a pluralityof different light color groups including a first light color, a secondlight color, and a third light color; the ultra-small LED electrodeassembly includes a mounting electrode line including a first mountingelectrode and a second mounting electrode, which are formed on the sameplane and spaced apart from each other, and ultra-small LED devicesincluding a first semiconductor layer and a second semiconductor layer,which each have one end in contact with the first mounting electrode andthe other end in contact with the second mounting electrode; and apercentage of the ultra-small LED devices, of which the firstsemiconductor layer is in direct or indirect contact with the firstmounting electrode, among all of the ultra-small LED devices in contactwith the mounting electrode is 60% or more.

The ultra-small LED device may have an aspect ratio of 1.2 to 100.Further, the ultra-small LED device may have a length of 100 nm to 10μm.

The ultra-small LED device may include a first semiconductor layer, anactive layer formed on the first semiconductor layer, a secondsemiconductor layer formed on the active layer, and an insulating thinfilm configured to cover at least an entire outer surface of the activelayer among outer surfaces of the ultra-small LED device. Here, onesemiconductor layer among the first semiconductor layer and the secondsemiconductor layer may include at least one N-type semiconductor layer,and the other semiconductor layer may include at least one P-typesemiconductor layer.

The ultra-small LED electrode assembly may have a luminance gain of 1.3or more according to Equation 2.

In the ultra-small LED electrode assembly, the number of the mountedultra-small LED devices per unit area (mm²) may be 1,000 or more.

The ultra-small LED electrode assembly may further include an insulatingfilm formed on outer surfaces of the first mounting electrode and thesecond mounting electrode and the plurality of ultra-small LED devicesmay come into contact with the first mounting electrode and the secondmounting electrode through the insulating film.

A percentage of the ultra-small LED devices, of which the firstsemiconductor layer is in contact with the first mounting electrode,among all of the ultra-small LED devices may be 80% or more.

The ultra-small LED electrode assembly may further include an ohmiclayer and portions in which the first and second mounting electrodes arein contact with end portions of each of the ultra-small LED devices.

Among the plurality of light color groups, the first light color may beblue, the second light color may be green, and the third light color maybe red. Here, the plurality of light color groups may further include afourth light color group of which a light color is white.

Hereinafter, the terms used in the present invention will be described.

In the description of embodiments according to the present invention,the term “mounting electrode line” may include any case of an electrodeline which is directly contactable with both end portions of anultra-small LED device, i.e., the ultra-small LED device issubstantially mountable thereon.

In the description of the embodiments according to the presentinvention, when each of layers, regions, patterns, or structures isdescribed as being formed “on,” “an upper portion of,” “above,” “under,”“a lower portion of,” or “below” a substrate, a layer, a region, or apattern, the terms “on,” “upper portion,” “above,” “under,” “lowerportion,” and “below” include the meaning of “directly” and“indirectly.”

In the description of the embodiments according to the presentinvention, the term “contact” refers that Component 1 is directlystructurally connected to Component 2 or is indirectly structurallyconnected to Component 2 through Component 3. For example, the term “afirst semiconductor layer in contact with a first mounting electrode”refers to the first semiconductor layer being directly structurallyconnected to the first mounting electrode and also refers to anelectrode layer being formed on the first semiconductor layer and theelectrode layer being directly structurally connected to the firstmounting electrode and thus the first semiconductor layer is indirectlyconnected to the first mounting electrode. Meanwhile, the term“structurally connected” does not refer to an electrical connectionstate related to whether an ultra-small LED device emits light whendriving power is applied to an electrode line, but refers to any case ofa physical contact state even when electrical connection is notestablished.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent to those of ordinary skill in theart by describing exemplary embodiments thereof in detail with referenceto the accompanying drawings, in which:

FIG. 1 is a schematic plan view illustrating a full-color light emittingdiode (LED) display according to one embodiment of the presentinvention;

FIGS. 2A and 2B are schematic plan views illustrating a full-color LEDdisplay according to one embodiment of the present invention, whereinFIG. 2A is a view illustrating a process of forming electrode lines in alattice form by separately disposing two electrode lines on differentplanes, and FIG. 2B is a view illustrating a process of forming twoelectrode lines in a lattice form on the same plane, wherein aninsulating layer is interposed between overlapping portions of the twoelectrode lines;

FIGS. 3A and 3B are views illustrating mounting electrode lines of anultra-small LED electrode assembly included in one embodiment of thepresent invention, wherein FIG. 3A is a view illustrating the mountingelectrode lines in which two mounting electrodes are alternatelydisposed, and FIG. 3B is a view illustrating the mounting electrodelines in which two mounting electrodes are alternately disposed in avortex form;

FIGS. 4A and 4B are views illustrating mounting electrode lines of anultra-small LED electrode assembly included in one embodiment of thepresent invention, wherein FIG. 4B is a view illustrating the mountingelectrode lines having an insulating partition wall surrounding edges ofthe mounting electrode lines shown in FIG. 4A;

FIG. 5 is a schematic view illustrating a method of manufacturing anultra-small LED electrode assembly provided in one embodiment of thepresent invention;

FIG. 6 is a schematic view illustrating a method of manufacturing anultra-small LED electrode assembly provided in one embodiment of thepresent invention;

FIGS. 7A to 7C are views illustrating an ultra-small LED electrodeassembly manufactured using a conventional method, wherein FIG. 7A is aperspective view of the ultra-small LED electrode assembly, FIG. 7B is alight emission picture when alternating current (AC) power is appliedthereto as driving power, and FIG. 7C is a light emission picture whendirect current (DC) power is applied thereto as the driving power;

FIGS. 8A to 8C are schematic views illustrating electrostatic attractionbetween an ultra-small LED device and mounting electrodes under anelectric field, wherein FIG. 8A is a schematic view before power isapplied to the mounting electrodes, FIG. 8B is a schematic view whensymmetric assembly power is applied to the mounting electrodes, and FIG.8C is a schematic view when asymmetric assembly power is applied to themounting electrodes;

FIG. 9 is a schematic view illustrating a method of manufacturing afull-color LED display according to one embodiment of the presentinvention;

FIGS. 10A to 10C are views illustrating an ultra-small LED electrodeassembly provided in one embodiment of the present invention, whereinFIG. 10A is a perspective view illustrating the ultra-small LEDelectrode assembly, FIG. 10B is a light emission picture when AC poweris applied thereto as driving power, and FIG. 10C is a light emissionpicture when DC power is applied thereto as the driving power;

FIG. 11 is a schematic view illustrating various shapes in whichmounting electrodes are in contact with both end portions of eachultra-small LED device in an ultra-small LED electrode assembly includedin one embodiment of the present invention;

FIGS. 12A and 12B are views illustrating an ultra-small LED electrodeassembly included in one embodiment of the present invention, whereinFIG. 12A is a light emission picture when AC power is applied thereto asdriving power, and FIG. 12B is a light emission picture when DC power isapplied thereto as the driving power;

FIG. 13 is a view illustrating an ohmic layer formed in an ultra-smallLED electrode assembly included in one embodiment of the presentinvention;

FIGS. 14A and 14B are views illustrating a full-color LED displayaccording to one embodiment of the present invention, wherein FIG. 14Ais a view illustrating an RGB LED display, and FIG. 14B is a viewillustrating an RGBW LED display; and

FIG. 15 is a graph illustrating assembly power applied to an ultra-smallLED electrode assembly provided in one embodiment of the presentinvention when the ultra-small LED electrode assembly is embodied.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings, whichwill be readily apparent to those skilled in the art to which thepresent invention belongs. The present invention may be embodied in manydifferent forms and is not limited to the embodiments described herein.In order to clearly illustrate the present invention in the followingdrawings, parts not related to the description will be omitted, and thesame reference numerals are used throughout the specification to referto the same or similar components.

A method of manufacturing a full-color light emitting diode (LED)display according to a first embodiment of the present invention mayinclude forming subpixels, each of which includes at least oneultra-small LED electrode assembly configured to emit light havingsubstantially the same light color.

Referring to FIG. 1, a method of manufacturing a display may includeforming a plurality of subpixels 1001, 1002, and 1003, and the subpixelmay be formed so that one or more ultra-small LED electrode assemblies100, 201, 202, 301, 302, 303, and 304 are provided in each of thesubpixels 1001, 1002, and 1003. For example, one ultra-small LEDelectrode assembly 100 may form one subpixel, e.g., a first subpixel1001. Alternatively, two ultra-small LED electrode assemblies 201 and202 may form one subpixel, e.g., a second subpixel 1002. Alternatively,four ultra-small LED electrode assemblies 301, 302, 303, and 304, mayform one subpixel, e.g., a third subpixel 1003. The number ofultra-small LED electrode assemblies provided in each subpixel may varyand may be implemented according to a total area and resolution of anembodied LED display and light efficiency of an LED device.

One or more ultra-small LED electrode assemblies provided in each of thesubpixels emit light having substantially the same light color. Here,the term “substantially the same light color” does not refer tocompletely the same wavelength of emitted light and refers to a lightcolor of light in a wavelength band in which light generally referred toas light having the same light color is included. For example, when thelight color is blue, all ultra-small LED electrode assemblies configuredto emit light in a wavelength band of 420 to 470 nm may be understood asemitting light having substantially the same light color. Further,“light color” refers to a light color of light emitted by an entireultra-small LED electrode assembly and does not refer to only lightcolor of light emitted by ultra-small LED devices provided in theultra-small LED electrode assembly. For example, when an ultra-small LEDelectrode assembly emits white light, the ultra-small LED electrodeassembly may be provided with all of ultra-small red LEDs, ultra-smallgreen LEDs, and ultra-small blue LEDs to emit light similar to whitelight or may be provided with only ultra-small blue LED devices andfurther provided with a yellow phosphor on the electrode assembly.

The ultra-small LED electrode assembly provided in the display accordingto the first embodiment of the present invention may emit blue light,white light, or ultraviolet (UV) light.

Meanwhile, an electrode arrangement of data electrodes, gate electrodes,and the like provided in a general display is not illustrated in FIG. 1,but the electrode arrangement used in the general display may be used asthe electrode arrangement which is not illustrated. Mounting electrodelines including a first mounting electrode and a second mountingelectrode, which is formed on the same plane as the first mountingelectrode and spaced apart from the first mounting electrode, may bedisposed at subpixel sites at which subpixels are formed according tothe electrode arrangement of the display. For example, the subpixels1001, 1002, and 1003 may be located in a region surrounded by electrodesin a lattice form electrode arrangement, as shown in FIG. 2A.

Meanwhile, in order to separately form the first mounting electrode andthe second mounting electrode on the same plane in the mountingelectrode lines provided in the ultra-small LED electrode assembly, whenan I^(th) electrode 1100 connected to the first mounting electrode (notshown) is a positive electrode (or a negative electrode) in FIG. 2A, anII^(th) electrode 1300 connected to the second mounting electrode (notshown) has to be a negative electrode (or a positive electrode).Therefore, in order to prevent a contact between the I^(th) electrode1100 and the II^(th) electrode 1300, the II^(th) electrode 1300 may beseparately disposed on the I^(th) electrode 1100, as shown in apartially enlarged cross-sectional view taken along line A-A′ of FIG.2A. Specifically, FIG. 3A is a view of an example of the mountingelectrode lines of the ultra-small LED electrode assembly provided atthe subpixel sites of the electrode arrangement shown in FIG. 2A, and afirst mounting electrode 110 is connected to the I^(th) electrode 1100disposed thereunder, a second mounting electrode 130 is disposed on thesame plane as the first mounting electrode 110, and the second mountingelectrode 130 and the I^(th) electrode 1100 are disposed in a latticeform, wherein the second mounting electrode 130 may be connected to theII^(th) electrode 1300 formed thereabove to prevent a mutual contactbetween the electrodes. Here, the first mounting electrode 110 and thesecond mounting electrode 130 may be separately disposed and may formmounting electrode lines P by being alternately disposed such that asmany ultra-small LED devices as possible are mounted thereon. Meanwhile,the first mounting electrode 110 and the second mounting electrode 130of the mounting electrode lines P shown in FIG. 3A may be changed into afirst mounting electrode 110′ and a second mounting electrode 130′separately disposed in a vortex form shown in FIG. 3B, and therefore, aspecific form of the mounting electrode lines may be changed accordingto a purpose thereof and the present invention is not particularlylimited to the above forms.

Alternatively, the I^(th) electrode 1100 and the II^(th) electrode 1300are disposed in a lattice form, as shown in FIG. 2B, wherein theelectrodes may be arranged so that an insulating layer 1601 isinterposed between overlapping portions of the I^(th) electrode 1100 andthe II^(th) electrode 1300 to prevent electrical short circuits as shownin a partially enlarged cross-sectional view taken along line B-B′.

Meanwhile, an electrode structure, an arrangement, a material, and thelike used in the display according to the present invention may bereplaced with those in a disclosure, i.e., Korean Patent RegistrationNo. 436123, made by the present inventor, and may also be replaced withan electrode structure, an arrangement, a material, and the like used ina general display, and thus the present invention may omit detaileddescriptions thereof.

Hereinafter, a method of manufacturing an ultra-small LED electrodeassembly by mounting ultra-small LED devices on mounting electrode linesformed at subpixel sites will be described in detail. The method ofmanufacturing an ultra-small LED electrode assembly may include (1)introducing a solution including a plurality of ultra-small LED devicesto mounting electrode lines including a first mounting electrode and asecond mounting electrode, which is formed on the same plane as thefirst mounting electrode and spaced apart from the first mountingelectrode, and (2) self-mounting the ultra-small LED devices by applyingpower having an asymmetric assembly voltage of 10 V or more according tothe following Equation 1 to the mounting electrode lines such that oneend of each of the ultra-small LED devices comes into contact with thefirst mounting electrode and the other end thereof comes into contactwith the second mounting electrode.

First, in operation (1), after mounting electrode lines P1, P2, and P3including the first mounting electrode 110 and the second mountingelectrode 130, which is formed on the same plane as the first mountingelectrode 110 and spaced apart from the first mounting electrode 110,are provided, as shown in FIG. 4A, the introduction of the solutionincluding the plurality of ultra-small LED devices is performed onmounting electrode lines P1, P1′, and P1″.

Specifically, FIG. 5A illustrates a solution 120 and 140, in which theplurality of ultra-small LED devices 120 are dispersed in a solvent 140,to be introduced to the mounting electrode line P1. Here, since aninsulating layer 1600 is disposed under the mounting electrode line P1,leakage of the solution under the mounting electrode line P1 may beprevented.

Meanwhile, when the solution 120 and 140 including the ultra-small LEDdevices is introduced to the mounting electrode line P1 as shown in FIG.5A, the solution does not stay on the mounting electrode line P1 andspreads outside of the mounting electrode line P1 when the solution 120and 140 is introduced. Therefore, there is a problem in that theultra-small LED devices are concentrated and disposed on edge portionsof the mounting electrode line or moved outside of the mountingelectrode line, and thus the ultra-small LED devices are not mounted onthe mounting electrode line and are useless. To solve the above problem,the ultra-small LED electrode assembly may further include an insulatingpartition wall 1700 surrounding edges of the mounting electrode line P2,as shown in FIG. 4B, or a solution 120′ and 141 including theultra-small LED devices is introduced to the insulating partition wall1700, as shown in FIG. 6A, to prevent the ultra-small LED devices frombeing disposed due to non-uniform spreading of the solution.

Meanwhile, detailed descriptions of a manufacturing method, a structure,the solvent introduced to the solution of the insulating partition wall,the number of the ultra-small LED devices in the solution, and the likemay be replaced with those in a disclosure, Korean Patent RegistrationNo. 2014-0085384, and thus the detailed description thereof in thepresent invention will be omitted.

According to one embodiment of the present invention, an insulating filmmay be further provided on outer surfaces of the first mountingelectrode and the second mounting electrode. Due to a distance betweenthe first mounting electrode and the second mounting electrode reduceddue to the insulating film, the ultra-small LED device may beself-mounted so that all of both ends thereof are located on the firstmounting electrode and the second mounting electrode. In this case, thenumber of ultra-small LED devices that can be mounted may be increaseddue to improvement of mounting alignment of the ultra-small LED devices,and a more highly-efficient ultra-small LED electrode assembly may beeasily implemented. Further, in step (2) described below, theultra-small LED devices may be introduced into the first mountingelectrode and the second mounting electrode in a mixed state with thesolvent. When power is applied to the ultra-small LED devices in orderto self-mount thereof, electrical short-circuit may occur between twodifferent mounting electrodes due to the solvent, and thus theelectrodes may be damaged. However, there is an advantage in thatelectrical short-circuit between the electrodes due to the solvent maybe prevented by the insulating film provided on the outer surfaces ofthe first mounting electrode and the second mounting electrode.

Next, in operation (2) of the present invention, the self-mounting ofthe ultra-small LED devices by power having an asymmetric assemblyvoltage of 10 V or more according to Equation 1 in accordance with thepresent invention being applied to the mounting electrode lines isperformed such that one end of each of the ultra-small LED devices comesinto contact with the first mounting electrode and the other end thereofcomes into contact with the second mounting electrode.

In operation (2), an electric field is formed in the mounting electrodelines, and components are moved to, arranged, and self-mounted on themounting electrode lines through various physical forces such aspolarization generated in the ultra-small LED devices, electrostaticattraction between the polarized ultra-small LED device and the mountingelectrode lines adjacent thereto, and the like under the electric field.However, in order to improve an orientation tendency of the ultra-smallLED devices to be mounted so that the devices are moved to and arrangedon electrodes and a first semiconductor layer in the device is incontact with the first mounting electrode, power having an asymmetricassembly voltage of 10 V or more according to Equation 1 has to beapplied to the mounting electrode lines.Asymmetric Assembly Voltage (V)=∥A(V)|−|B(V)∥  [Equation 1]

Here, A indicates a magnitude of an upper end of a peak voltage of theapplied power, and B indicates a magnitude of a lower end of the peakvoltage thereof.

In a conventional ultra-small LED electrode assembly made by the presentinventor, power applied in operation (2) had a symmetric assemblyvoltage of 0 V according to Equation 1. However, since an orientation bywhich one specific end of each ultra-small LED device is in contact witha specific mounting electrode was randomly determined when such asymmetric assembly voltage was used, the ultra-small LED devices werenot mounted to have proper orientation, and thus alternating current(AC) power had to be used as driving power. Specifically, FIG. 7A is aschematic view illustrating an ultra-small LED electrode assemblyimplemented using a symmetric assembly voltage of 0 V according toEquation 2, and it was determined that the ultra-small LED electrodeassembly may emit light when AC power was used as the driving power, asshown in FIG. 7B. However, when direct current (DC) power different fromthe above driving power was applied to an ultra-small LED electrodeassembly which was the same as that implemented using the symmetricassembly voltage shown in FIG. 7B, it was determined that emissionefficiency was different from that shown in FIG. 7B and wassignificantly decreased, as shown in FIG. 7C. This result means that aproblem occurred when the ultra-small LED electrode assembly implementedusing the symmetric assembly voltage shown in FIG. 7A used the DC poweras the driving power.

The reason for a decrease in luminance when DC driving power is appliedas shown in FIG. 7C is that there is no orientation tendency betweendifferent mounting electrodes in direct or indirect contact withdifferent semiconductors (e.g., a P-type semiconductor and an N-typesemiconductor) of an ultra-small LED device in the electrode assembly.Specifically, as shown in FIG. 7A, among eight ultra-small LED devicesmounted on the ultra-small LED electrode assembly, the number ofdevices, which are identical to a first ultra-small LED device 21, incontact with the first mounting electrode 10 is four, and the remainingfour ultra-small LED devices, which are different from the firstultra-small LED device 21, are in contact with the first mountingelectrode 10. Therefore, when unidirectional DC driving power is appliedto the ultra-small LED electrode assembly shown in FIG. 7A, only fourultra-small LED devices emit light, and the remaining four ultra-smallLED devices do not emit light, and thus a luminance of the ultra-smallLED electrode assembly is lowered.

In conclusion, when the conventional method of applying a symmetricassembly voltage to ultra-small LED devices and self-aligning theultra-small LED devices is used, both end portions of each of theultra-small LED devices are only in contact with two differentelectrodes, and the ultra-small LED devices may not be mounted on themounting electrodes with a desired orientation therebetween. Therefore,in all probability, an ultra-small LED electrode assembly that exhibitshigh luminance using DC driving power cannot be manufactured.

However, when an asymmetric voltage is used instead of a symmetricvoltage and power having an asymmetric voltage of 10 V or more accordingto Equation 1 in accordance with the present invention for a degree ofasymmetry of the asymmetric voltage is applied to the ultra-small LEDelectrode assembly, an orientation between the ultra-small LED devicesand the mounting electrodes may be desirably adjusted, and thus adisplay can be driven using DC driving power and the driven display canalso exhibit very excellent luminance characteristics.

The orientation between ultra-small LED devices and mounting electrodes,which is affected by the asymmetric voltage, will be described withreference to FIG. 8. Specifically, FIG. 8A shows a state immediatelyafter operation (1) is performed, and shows an ultra-small LED device120 provided with a first semiconductor layer 120 b and a secondsemiconductor layer 120 d disposed on mounting electrode lines 110 and130. Although not shown in FIG. 8A, the ultra-small LED device 120 ismixed into a solvent. In order to mount the ultra-small LED device in astate of FIG. 8A, voltages (V_(AC)=±30 V) of which peaks are symmetricare conventionally applied to the first mounting electrode 110 and thesecond mounting electrode 130, as shown in FIG. 8B, and, in this case,magnitudes a1 and a2 of electrostatic attraction, which is applied tothe ultra-small LED device and shown in FIG. 8B, of the two electrodesmay be the same when lengths of the first semiconductor layer 120 b andthe second semiconductor layer 120 d are the same and all otherinfluences around the layers are not considered. Here, a probability ofthe first semiconductor layer 120 b coming into contact with the firstmounting electrode 110 may be 50%. In a broader sense, the firstsemiconductor layer 120 b of each of the plurality of ultra-small LEDdevices introduced to the mounting electrode may come into contact withthe first mounting electrode 110 at about a 50% probability, and aprobability of a total of 10 ultra-small LED devices being mounted andcoming into contact with the first mounting electrode 110 may be only(0.5)¹⁰.

However, when asymmetric voltages are applied to the first mountingelectrode 110 and the second mounting electrode 130, as shown in FIG.8C, polarization of a surface of the ultra-small LED device is formeddifferently from that of FIG. 8B, and thus electrostatic attraction b 1and b2, which moves the first semiconductor layer 120 b toward the firstmounting electrode 110 and moves the second semiconductor layer 120 dtoward the second mounting electrode 130, is strengthened, a probabilityof the first semiconductor layer 120 b coming into contact with thefirst mounting electrode 110 is further increased, and, in a broadersense, the plurality of ultra-small LED devices introduced to themounting electrode may have a proper orientation and may more easilycome into contact with the first mounting electrode.

However, immediately after operation (1) is performed, all of theultra-small LED devices are not disposed in parallel between the twoelectrode, as shown in FIG. 8A. Some of the ultra-small LED devices maybe obliquely disposed with different slopes, or some of the ultra-smallLED devices may be disposed on one of the mounting electrodes. Further,the semiconductor layers included in the ultra-small LED devices may beasymmetrically formed and have different lengths. Therefore, in order tofurther improve an orientation tendency of a specific semiconductorlayer of the ultra-small LED device coming into contact with a specificmounting electrode in consideration of the above states, an asymmetricvoltage of assembly power applied to the mounting electrodes has to be10 V or more according to Equation 1 and may preferably be 14 V or more,more preferably be 18 V or more, and most preferably be 25 V or more.When the asymmetric assembly voltage according to Equation 1 is lessthan 10 V, the orientation tendency of the specific semiconductor layerof the ultra-small LED device coming into contact with the specificmounting electrode is decreased, a luminance of some of the manufacturedultra-small LED electrode assemblies is significantly degraded when DCdriving power is applied to the manufactured ultra-small LED electrodeassemblies in comparison to when AC driving power is applied thereto,and thus luminances of subpixels may be different from each other, and,as a result, a resolution, color reproducibility, or the like of animage may be degraded. Meanwhile, when the asymmetric assembly voltageaccording to Equation 1 is more than 50 V, there is no problem regardingorientation of a specific direction of the ultra-small LED device, butthe electrodes may be damaged.

Here, in the Equation 1, A and B do not refer to voltages applied to thefirst mounting electrode and the second mounting electrode,respectively. That is, when power having 30 V and power having 0 V arerepeatedly applied to the first mounting electrode in a predeterminedcycle and power having 0 V and power having 30 V are repeatedly appliedto the second mounting electrode in the predetermined cycle, the powerapplying method is the same as the manner in which voltages of +30 V and−30 V are applied to the mounting electrode lines as a pulse wave in thepredetermined cycle. Further, in this case, a value according toEquation 1 is zero, and symmetric voltages are applied to the mountingelectrode lines.

Further, according to one embodiment of the present invention, the powermay be power having the predetermined cycle and may be power in a sinewaveform preferably having a frequency of 50 kHz to 1 GHz, and morepreferably having a frequency of 90 kHZ to 100 MHz.

When the power is applied to the mounting electrodes without a cycle,i.e., a predetermined constant voltage is continuously applied thereto,the mounting electrodes may be damaged even when the above-describedEquation 1 is satisfied, and the mounted ultra-small LED device may notbe driven by the mounting electrodes when the damage is high.

Further, when the frequency is lower than 50 kHz, the number of mountedultra-small LED devices is significantly decreased even when the voltagerange is satisfied, an orientation of the devices is very irregular, andthus DC power may not be used as driving power. Further, when thefrequency is higher than 1 GHz, the ultra-small LED devices may notadapt to a rapidly changing power, mountability of the devices isdegraded, the orientation thereof is also degraded, and thus DC powercannot be used as driving power, like in the case of low frequencies.

Meanwhile, an effective voltage (Vrms) of the above-described power maypreferably be 12 V or more, and may more preferably be 17 V or more,because the number of mounted ultra-small LED devices may be decreasedwhen the effective voltage of the power is low. That is, when anultra-small LED electrode assembly is embodied by power which satisfiesa value according to the above-described Equation 1 being appliedthereto, the ultra-small LED electrode assembly may be driven by DCpower due to an increased mounting tendency of a specific semiconductorlayer of the ultra-small LED device being electrically connected to aspecific mounting electrode, but, since the number of the mountedultra-small LED devices is low, an amount of emitted light may besignificantly small when driving power is applied to the ultra-small LEDelectrode assembly.

Meanwhile, as operation (3), after operation (2) is performed, a thermalprocess may be further performed on the ultra-small LED devicesself-mounted on the mounting electrode lines at a temperature of 200 to1000° C., preferably in the range of 300 to 1,000° C., and morepreferably in the range of 600 to 1,000° C., for 0.5 to 10 minutes. Thethermal process is a process of removing the introduced solvent whicheasily moves and arranges the ultra-small LED devices after theultra-small LED devices are in contact with different mountingelectrodes. In a state in which the solvent is not completely removed,when driving power is applied or an ohmic layer configured to decrease acontact resistance between the mounting electrodes and the ultra-smallLED devices is formed, the ultra-small LED electrode assembly may have alow emission efficiency which is lower than a targeted level. Further,the remaining solvent causes defects during a process of forming theohmic layer, and even when the ohmic layer is formed, the level of theformation may be low and a large current loss may occur. When thethermal process is performed at a temperature of 200° C. or lower and/orfor 0.5 minutes or less, a problem in that impurities are not completelyremoved and a problem in that a contact reaction between the ultra-smallLED devices and the mounting electrodes are not completed may occur, andwhen the thermal process is performed at a temperature of more than1,000° C. and/or for more than 10 minutes, a problem in that a basesubstrate and/or electrodes are deformed or broken and a problem in thata voltage is not suitably applied to the ultra-small LED devices due toan increased resistance may occur. Further, operation (3) is preferablyperformed again after the ohmic layer is formed, which will bedescribed. Accordingly, an ultra-small LED electrode assembly havingimproved emission efficiency can be embodied, and a luminance of theembodied LED display can be improved.

Meanwhile, the method of manufacturing an ultra-small LED electrodeassembly provided in an LED display according to one exemplarilyembodiment of the present invention may further include simultaneouslyforming an ohmic layer and contact portions of the first and secondmounting electrodes and the ultra-small LED device after theabove-described operation (2) is performed. The forming of the ohmiclayer is preferably performed after the above-described operation (3) isperformed.

The reason for simultaneously forming an ohmic layer 1800 and a contactportion S, as shown in FIG. 13, is to further improve emissionefficiency by reducing a contact resistance generated between themounting electrodes and the ultra-small LED devices when driving poweris applied thereto. Since the ohmic layer can be made using any knowngeneral methods in the art without limitation, the present invention isnot limited to a specific method, and a description thereof will beomitted. Further, a known material, e.g., gold (Au), may be used as amaterial of the ohmic layer.

Meanwhile, in the full-color LED display according to the firstembodiment of the present invention, ultra-small LED electrodeassemblies provided in subpixels may emit blue light, white light, or UVlight, and, in this case, a process of forming a color conversion layer,which is capable of converting emitted light into light having a lightcolor different from a light color of the emitted light for implementinga color image, on the subpixels may be further performed on thefull-color LED display.

Preferably, color reproducibility may be improved by further enhancingcolor purity, a short-wavelength transmission filter may be formed onthe subpixel to improve emission efficiency of color converted light,e.g., green light or red light, of a front surface thereof so that lightemission is changed from a rear surface of the color conversion layer tothe front surface, and the color conversion layer may be formed in oneregion of an upper portion of the short-wavelength transmission filter.

The above will be described on the basis of a display implemented withsubpixels including ultra-small LED electrode assemblies which emit bluelight. Specifically, a passivation layer 1910 is formed as shown in FIG.9B to simultaneously planarize and insulate upper portions of subpixelson which a metal ohmic layer is formed, as shown in FIG. 9A, and then ashort-wavelength transmission filter 1920 may be formed on thepassivation layer 1910, as shown in FIG. 9C. The short-wavelengthtransmission filter 402 may be a multilayer film in which thin filmsmade of highly refractive and slightly refractive materials arerepeatedly formed, and a composition of the multilayer film may be[(0.125)SiO₂/(0.25)TiO₂/(0125)SiO₂]_(m) (m=the number of repeatedlayers, and m is 5 or more) to transmit blue light and reflect lighthaving a wavelength longer than the blue light. Further, theshort-wavelength transmission filter 402 may have a thickness of 0.5 to10 but is not limited thereto. A method of forming the short-wavelengthtransmission filter 1920 may be one method of an e-beam method, asputtering method, and an atomic layer deposition (ALD) method, but isnot limited thereto.

Next, a process of forming color conversion layers 1930 and 1940 may beperformed on the short-wavelength transmission filter 1920, as shown inFIG. 9D. Specifically, the color conversion layers 1930 and 1940 may beformed by patterning a green color conversion layer 1930 on theshort-wavelength transmission filter corresponding to some subpixelsselected among the subpixels and patterning a red color conversion layer1940 on the short-wavelength transmission filter corresponding to somesubpixels selected among the remaining subpixels. A method of formingthe patterns may be performed by one or more methods selected from thegroup of a screen printing method, a photolithography method, and adispensing method. Meanwhile, a patterning order of the green colorconversion layer and the red color conversion layer has no limitation,and the layers may be simultaneously formed or may be formed in areversed order. Further, the red color conversion layer 1940 and thegreen color conversion layer 1930 may include a color conversionmaterial such as a phosphor or the like which is excited by lightemitted from a color conversion layer, e.g., a color filter, orultra-small LED electrode assemblies known in light and display fieldsand converts the light into light having a desired light color, or mayinclude a known color conversion material. For example, the green colorconversion layer 1930 may be a phosphor layer including a greenphosphor, and specifically, may include one or more phosphors selectedfrom the group of SrGa₂S₄:Eu, (Sr,Ca)₃SiO₅:Eu, (Sr,Ba,Ca)SiO₄:Eu,Li₂SrSiO₄:Eu, Sr₃SiO₄:Ce,Li, β-SiALON:Eu, CaSc₂O₄:Ce, Ca₃Sc₂Si₃O₁₂:Ce,Caα-SiALON:Yb, Caα-SiALON:Eu, Liα-SiALON:Eu, Ta₃Al₅O₁₂:Ce, Sr₂Si₅N₈:Ce,(Ca, Sr,Ba)Si₂O₂N₂:Eu, Ba₃Si₆O₁₂N₂:Eu, γ-AlON:Mn, and γ-AlON:Mn,Mg, butis not limited thereto. Further, the red color conversion layer 1940 maybe a phosphor layer including a red phosphor, and specifically, mayinclude one or more phosphors selected from the group of(Sr,Ca)AlSiN₃:Eu, CaAl SiN₃:Eu, (Sr,Ca)S:Eu, CaSiN₂:Ce, SrSiN₂:Eu,Ba₂Si₅N₈:Eu, CaS:Eu, CaS:Eu,Ce, SrS:Eu, SrS:Eu,Ce, and Sr₂Si₅N₈:Eu, butis not limited thereto.

When an LED display substrate manufactured as shown in FIG. 9D is viewedfrom a vertical top thereof, only a short-wavelength transmission filteris disposed on the uppermost layer and a green color conversion layerand a red color conversion layer are not formed at some subpixel sites,and thus blue light may be incident on the some subpixel sites. Inaddition, green light may be incident on some subpixel regions at whichthe green color conversion layer 1930 is formed on the short-wavelengthtransmission filter through the green conversion layer. Further, sincethe red color conversion layer 1940 is formed on the short-wavelengthtransmission filter at the remaining subpixel sites, red light may beincident on the remaining subpixel sites, and thus a color-by-blue LEDdisplay can be embodied.

A long-wavelength transmission filter 1950 may preferably be formed onan upper portion of the display substrate including the green and redcolor conversion layers 1930 and 1940, as shown in FIG. 9E.

An insulating layer (not shown) may preferably be formed on theshort-wavelength transmission filter 1920 including the patterned colorconversion layers 1930 and 1940 before the long-wavelength transmissionfilter 1950 is formed. Further, stepped portions are made because ofsteps between a portion on which the green or red color conversion layeris formed and a portion on which the green or red color conversion layeris not formed, as shown in FIG. 9D, but the stepped portions may becoated with and planarized by the insulating layer. The insulating layermay be formed of one material of spin-on-glass (SOG), a transparentpolymer, and a transparent dielectric paste using a spin coating orscreen printing method, but is not limited thereto. The formedinsulating layer may have a thickness of 10 to 100 μm, but is notlimited thereto.

Then, the long-wavelength transmission filter 1950 may be formed asshown in FIG. 9E to prevent degradation of color purity above theinsulating layer by mixing blue light emitted from the ultra-small blueLEDs and green and red light emitted from the green and red colorconversion layers. The long-wavelength transmission filter 1950 may beformed on all or a part of the green color conversion layer 1930 and thered color conversion layer 1940, and may preferably be formed on onlythe green and red color conversion layers. The long-wavelengthtransmission filter 1950 used herein may be a multilayer film in whichthin films made of highly refractive and slightly refractive materials,which are capable of achieving the purpose of transmission of lighthaving a long wavelength and reflection of light having a shortwavelength to reflect blue light, are repeatedly formed, and acomposition of the multilayer film may be[(0.125)SiO₂/(0.25)TiO₂/(0125)SiO₂]_(m) (m=the number of repeatedlayers, and m is 5 or more). Further, the long-wavelength transmissionfilter 1950 may have a thickness of 0.5 to 10 but is not limitedthereto. A method of forming the long-wavelength transmission filter1950 may be one method of an e-beam method, a sputtering method, and anALD method, but is not limited thereto. Further, in order to form thelong wavelength transmission filter on only the green and red colorconversion layers, the long wavelength transmission filter may be formedin a desired region using a metal mask capable of exposing the green andred color conversion layers and masking the other regions excluding theexposed areas.

The full-color LED display according to the first embodiment of thepresent invention which is embodied using the above-describedmanufacturing method has an improved orientation tendency between onespecific end of the ultra-small LED device and a specific mountingelectrode line. Therefore, the embodied full-color LED display includessubpixels, each of which includes at least one ultra-small LED electrodeassembly configured to emit light having substantially the same lightcolor, and the ultra-small LED electrode assembly includes mountingelectrode lines including a first mounting electrode and a secondmounting electrode which are formed on the same plane and spaced apartfrom each other, ultra-small LED devices including a first semiconductorlayer and a second semiconductor layer, which each have one end incontact with the first mounting electrode and the other end in contactwith the second mounting electrode, wherein a percentage of theultra-small LED devices, of which the first semiconductor layer is indirect or indirect contact with the first mounting electrode, among allof the ultra-small LED devices in contact with the mounting electrode issatisfied as 60% or more.

Specifically, FIG. 10A is a schematic view illustrating one ultra-smallLED electrode assembly provided in a subpixel, wherein the ultra-smallLED electrode assembly is embodied to include electrode lines includinga first mounting electrode 110 and a second mounting electrode 130,which are formed on the same plane and spaced apart from each other, anda plurality of ultra-small LED devices 121 and 122, which each have oneend in contact with the first mounting electrode and the other end incontact with the second mounting electrode.

In an ultra-small LED electrode assembly such as that shown in FIG. 10A,since the first mounting electrode 110 and the second mounting electrode130 are located on the same plane, the ultra-small LED devices 121 and122 are connected to the electrodes while in lying postures, and sincenanometer-sized ultra-small LED devices need not be three-dimensionallyupright to be coupled to the electrodes, the number of deviceselectrically connected to the electrodes are increased. Further, sincean amount of photons generated inside the ultra-small LED device, whichare blocked by electrodes, not extracted, and dissipated, is minimized,light extraction efficiency of the ultra-small LED device can beimproved, and an LED display having an improved luminance can besuitably embodied.

Although both of the end portions of each of the ultra-small LED devices121 and 122 are in contact with two the mounting electrodes 110 and 130in FIG. 10A, both of the end portions of each of the ultra-small LEDdevice may be variously in contact with two mounting electrodes, asshown in FIG. 11. Specifically, a first ultra-small LED device 123 ismounted so that both end portions thereof are in contact with upperportions of a first mounting electrode 111 and a second mountingelectrode 131, one end portion of a second ultra-small LED device 124 isin contact with an upper portion of the second mounting electrode 131and the other end portion thereof is in contact with a side surface ofanother first mounting electrode 112. Further, both end portions of athird ultra-small LED device 125 are in contact with side surfaces ofthe other first mounting electrode 112 and another second mountingelectrode 132. As shown in FIG. 11, in the ultra-small LED electrodeassembly included in one embodiment of the present invention, oneultra-small LED electrode assembly may have various contact forms inwhich an ultra-small LED device is inserted into a separate spacebetween two mounting electrodes and is in contact with the two mountingelectrodes or in which the ultra-small LED device is in contact withupper portions of the two mounting electrodes. Alternatively, amultilayer may be formed in the separate space between the two mountingelectrodes and the ultra-small LED device may be inserted into themultilayer to come into contact with the two mounting electrodes.Therefore, the contact forms are not limited to those shown in FIG. 11.

Meanwhile, since the ultra-small LED device mounted in one ultra-smallLED electrode assembly included in the present invention is embodied sothat about 60% or more of all of the mounted ultra-small LED deviceshave an orientation tendency of the same semiconductors, e.g., the firstsemiconductor layers, coming into contact with one electrode, e.g., thefirst mounting electrode, even when AC power is not used as drivingpower and DC power is used as the driving power, 60% or more of all ofthe mounted ultra-small LED devices may emit light, and thus sufficientluminance characteristics can be exhibited. When less than 60% of all ofthe mounted ultra-small LED devices have a unidirectional orientation, aluminance exhibited when DC power is used as the driving power issignificantly degraded in comparison with a luminance exhibited when ACpower is used as the driving power, and thus driving the LED display byusing DC driving power is difficult. A percentage of the ultra-small LEDdevices which each have the first semiconductor layer in direct orindirect contact with the first mounting electrode among all of themounted ultra-small LED devices in one ultra-small LED electrodeassembly may preferably be 80% or more, and thus more improved luminancecharacteristics can be exhibited.

Further, in the ultra-small LED electrode assembly provided in the LEDdisplay according to one embodiment of the present invention, the numberof mounted ultra-small LED devices per unit area (mm²) is 1,000 or more,and thus a display having very excellent luminance characteristics canbe embodied. Meanwhile, an average number of mounted ultra-small LEDdevices per unit area is not related to a total area including electroderegions in which the ultra-small LED devices are not substantiallymounted, and refers to the number of mounted ultra-small LED devices perunit area which is converted from the number of mounted ultra-small LEDdevices on the basis of an area of mounting electrode lines on which theultra-small LED devices are substantially mounted.

Meanwhile, any ultra-small LED device generally used in an LED displaymay be used for the ultra-small LED device provided in the ultra-smallLED electrode assembly without limitation. A length of the ultra-smallLED device may preferably be in the range of 100 nm to 10 μm, and maymore preferably be in the range of 500 nm to 5 μm. When the length ofthe ultra-small LED device is less than 100 nm, manufacturing an LEDdevice having high efficiency may be difficult, and when the length isgreater than 10 μm, light emission efficiency of the LED device may bedegraded. The ultra-small LED device may have various shapes, such as acylindrical shape, a rectangular shape, etc., and may preferably have acylindrical shape, but the shape is not limited to the above-describedshapes. Further, an aspect ratio of the ultra-small LED device may be inthe range of 1.2 to 100, preferably in the range of 1.2 to 50, morepreferably in the range of 1.5 to 20, and especially preferably in therange of 1.5 to 10. When the aspect ratio of the ultra-small LED deviceis less than 1.2, the ultra-small LED devices may not be self-alignedeven when power is applied to electrode lines, and when the aspect ratiois more than 100, a voltage of power for self-aligning the ultra-smallLED devices may be low, but a process of manufacturing a device havingan aspect ratio of more than 100 may be difficult due to processlimitations during a process of manufacturing the ultra-small LEDdevices using a dry etching process and the like.

Further, the ultra-small LED device may include a first semiconductorlayer and a second semiconductor layer, and more preferably, may includethe first semiconductor layer, an active layer formed on the firstsemiconductor layer, the second semiconductor layer formed on the activelayer, and an insulating thin film configured to cover at least anentire outer surface of the active layer among outer surfaces of theultra-small LED device.

Here, one semiconductor layer among the first semiconductor layer andthe second semiconductor layer may include at least one N-typesemiconductor layer, and the other semiconductor layer may include atleast one P-type semiconductor layer. For example, when an ultra-smallLED device is a blue light emission device, the N-type semiconductorlayer may be one or more selected from InAlGaN, GaN, AlGaN, InGaN, AlN,InN, and the like, which are semiconductor materials having acompositional formula of In_(x)Al_(y)Ga_(1-x-y)N (0≤x≤1, 0≤y≤1, and0≤(x+y)≤1), and may be doped with a first conductive dopant such as Si,Ge, Sn, etc. The N-type semiconductor layer may preferably have athickness of 500 nm to 5 μm, but is not limited thereto. Emitted lightof the ultra-small LED is not limited to blue light, and thus, in thecase of different emitted light colors, there is no limitation in usinga different type of III-V group semiconductor material in the N-typesemiconductor layer. Further, the P-type semiconductor layer may be oneor more selected from InAlGaN, GaN, AlGaN, InGaN, AN, InN, and the like,which are semiconductor materials having a compositional formula ofIn_(x)Al_(y)Ga_(1-x-y)N (0≤x≤1, 0≤y≤1, and 0≤(x+y)≤1), and may be dopedwith a second conductive dopant such as Mg. The P-type semiconductorlayer may preferably have a thickness of 500 nm to 5 μm, but is notlimited thereto. Emitted light of the ultra-small LED is not limited toblue light, and thus, in the case of different emitted light colors,there is no limitation in using a different type of III-V groupsemiconductor material in the P-type semiconductor layer.

The active layer may be interposed between the first semiconductor layerand the second semiconductor layer and, when an electric field isapplied to a device, the active layer generates light because electronsare coupled to holes. The active layer may be formed with one ormultiple quantum well structures. Clad layers doped with a conductivedopant may be formed on and/or under the active layer, and the cladlayers doped with the conductive dopant may be embodied as an AlGaNlayer or InAlGaN layer. Alternatively, a material, such as AlGaN,AlInGaN, or the like, may also be used as the active layer. The activelayer may preferably have a thickness of 10 to 200 nm, but is notlimited thereto. The active layer may be formed to be located at anylocation according to types of LEDs. A light color of the ultra-smallLED device is not limited to blue, and thus, in the case of differentemitted light colors, there is no limitation in using a different typeof III-V group semiconductor material in the active layer.

Electrode layers may be further formed on the first semiconductor layerand/or under the second semiconductor layer. When the semiconductorlayer further includes the electrode layer, a contact of a mountingelectrode and an ultra-small LED device may be formed between theelectrode layer and the mounting electrode and/or between both theelectrode and semiconductor layers and the mounting electrode. Theelectrode layer may be formed of a metal or metal oxide generally usedfor an electrode of an LED device, and may preferably be formed of oneor a combination of chrome (Cr), titanium (Ti), aluminum (Al), gold(Au), nickel (Ni), indium tin oxide (ITO), and an oxide or alloythereof, but the present invention is not limited thereto. The electrodelayer may preferably have a thickness of 1 to 100 nm, but is not limitedthereto. When the semiconductor layer includes the electrode layer, theelectrode layer and the mounting electrode may be joined at atemperature lower than a temperature required in a process of forming ametal ohmic layer on a contact portion of the semiconductor layer andthe mounting electrode.

At least an outer surface of the ultra-small LED device and the activelayer may be coated with the insulating thin film, and more preferably,one or more of the first semiconductor layer and the secondsemiconductor layer may be coated with the insulating thin film, toprevent durability of the ultra-small LED device from being degraded dueto damage of an outer surface of the semiconductor layer. The insulatingthin film may serve to prevent electrical short circuits generated inthe ultra-small LED device when the active layer included in theultra-small LED device comes into contact with the mounting electrode.Further, the insulating thin film protects the outer surface of theultra-small LED device and the active layer, and thus surface defects ofthe active layer are prevented and a decrease in emission efficiency canbe prevented. The insulating thin film may preferably include one ormore of silicon nitride (Si₃N₄), aluminum oxide (Al₂O₃), hafnium oxide(HfO₂), yttrium oxide (Y₂O₃), and titanium dioxide (TiO₂), and morepreferably, may include transparent materials of the above components,but the present invention is not limited thereto. A transparentinsulating thin film may serve as the insulating thin film, and adecrease in emission efficiency which may occur may also be minimized byusing the ultra-small LED device coated with the insulating thin film.

Further, since the ultra-small LED electrode assembly provided in thefull-color LED display according to the above-described first embodimenthas an improved orientation tendency between one specific end of theultra-small LED device and a specific mounting electrode line, oneultra-small LED electrode assembly provided in each subpixel may have asatisfied luminance gain of 1.1 or more according to the followingEquation 2, and may preferably have a satisfied luminance gain of 1.3 ormore.

$\begin{matrix}{{{Luminance}\mspace{14mu}{Gain}} = \frac{\begin{matrix}{{Luminance}\mspace{14mu}{of}\mspace{14mu}{ultra}\text{-}{small}\mspace{14mu}{LED}\mspace{14mu}{electrode}} \\{{assembly}\mspace{14mu}{driven}\mspace{14mu}{by}\mspace{14mu}{DC}\mspace{14mu}{voltage}\mspace{14mu}\left( {{cd}\text{/}m^{2}} \right)}\end{matrix}}{\begin{matrix}{{Luminance}\mspace{14mu}{of}\mspace{14mu}{ultra}\text{-}{small}\mspace{14mu}{LED}\mspace{14mu}{electrode}} \\{{assembly}\mspace{14mu}{driven}\mspace{14mu}{by}\mspace{14mu}{AC}\mspace{14mu}{voltage}\mspace{14mu}\left( {{cd}\text{/}m^{2}} \right)}\end{matrix}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Equation 2 shows a parameter for a relative ratio with respect toluminance measured in an ultra-small LED electrode assembly when DCpower and AC power are applied to the same single ultra-small LEDelectrode assembly as driving power and a magnitude of a DC voltage (V)is 0.5 times amplitude of an AC voltage (V). As the luminance gain has avalue greater than one, the DC power may drive the ultra-small LEDelectrode assembly as the driving power, improved luminancecharacteristics may also be exhibited, and a luminance exhibited by eachsubpixel may also be more uniform.

Specifically, the following Comparative Example 1 relates to anultra-small LED electrode assembly manufactured using a conventionalmanufacturing method. An area of a graph measured for each wavelengthwhen DC power having a waveform of 21.2 V without a cycle was applied tothe ultra-small LED electrode assembly as driving power was merely 0.51times an area of a graph measured for each wavelength when AC powerhaving a peak voltage of ±21.2 V and in a sine wave form having afrequency of 60 Hz was applied thereto as the driving power. Regardingintensity of light maximally emitted by the ultra-small LED electrodeassembly, the intensity of light when the DC power was applied to theultra-small LED electrode assembly as the driving power was merely about0.52 times the intensity of light when the AC power was applied theretoas the driving power. Therefore, the luminance and the intensity of thelight in a specific wavelength band were significantly degraded (seeTable 1).

Compared to the above, in the case of an ultra-small LED electrodeassembly manufactured using one embodiment of the present invention (seeExample 2), an area of a graph measured for each wavelength when DCpower having a waveform of 21.2 V without a cycle was applied to theultra-small LED electrode assembly as driving power was significantlyincreased to be 1.12 times an area of a graph measured for eachwavelength when AC power having a peak voltage of ±21.2 V and in a sinewave form having a frequency of 60 Hz was applied thereto as the drivingpower. Regarding intensity of light maximally emitted by the ultra-smallLED electrode assembly, the intensity of the light when the DC power wasapplied to the ultra-small LED electrode assembly as the driving powerwas significantly increased to be about 1.19 times the intensity oflight when the AC power was applied thereto as the driving power.

Further, in the case of an ultra-small LED electrode assemblymanufactured using another embodiment of the present invention (seeExample 1), an area of a graph measured for each wavelength when DCpower having a waveform of 21.2 V without a cycle was applied to theultra-small LED electrode assembly as driving power was significantlyincreased to be 1.43 times an area of a graph measured for eachwavelength when the AC power having a peak voltage of ±21.2 V and in asine wave form having a frequency of 60 Hz was applied thereto as thedriving power. Regarding intensity of light maximally emitted by theultra-small LED electrode assembly, the intensity of the light when theDC power was applied to the ultra-small LED electrode assembly as thedriving power was significantly increased to be about 1.47 times theintensity of light when the AC power was applied thereto as the drivingpower.

Meanwhile, a full-color LED display according to a second embodiment ofthe present invention is manufactured using the following manufacturingmethod so that a full-color image is embodied without including colorconversion layers, unlike the first embodiment.

Specifically, the method includes forming subpixels, each of whichincludes at least one ultra-small LED electrode assembly configured toemit light having substantially the same light color, wherein the lightcolor is divided into a plurality of different light color groupsincluding a first light color, a second light color, and a third lightcolor. The ultra-small LED electrode assembly may be manufactured by (a)introducing a solution including ultra-small LED devices to a mountingelectrode line including a first mounting electrode and a secondmounted, which is an electrode formed on the same plane as the firstmounting electrode and spaced apart from the first mounting electrode,and (b) self-mounting the plurality of ultra-small LED devices byapplying power, which has an asymmetric assembly voltage of 10 V or moreaccording to Equation 1, to the mounting electrode line such that oneend of each of the ultra-small LED devices comes into contact with thefirst mounting electrode and the other end thereof comes into contactwith the second mounting electrode.

There is a difference between color implementation methods of thefull-color LED display according to the second embodiment and thefull-color LED display according to the first embodiment, andspecifically, the subpixels are embodied so that light color is dividedinto the plurality of different light color groups including the firstlight color, the second light color, and the third light color. Each ofthe subpixels may include one or more ultra-small LED electrodeassemblies, each of which exhibits one light color among the first lightcolor, the second light color, and the third light color.

As an example of the first light color, the second light color, and thethird light color, the first light color may be blue 403, the secondlight color may be green 402, and the third light color may be red 401,as shown in FIG. 14A, and thus an R-G-B LED display can be embodied.Alternatively, the light color group may further include a fourth lightcolor group which has a light color of white 504, as shown in FIG. 14B,thus an R-G-B-W LED display can be embodied, and thereby an LED displayhaving more improved color reproducibility can be embodied.

The method of manufacturing of a full-color LED display according to thesecond embodiment may have substantially the same applied asymmetricvoltage conditions as the manufacturing method according to theabove-described first embodiment.

However, the above methods may have a difference in that ultra-small LEDelectrode assemblies provided in adjacent subpixels are made to emitlight having different light colors. For example, first subpixels 403and 503 configured to emit blue light may be embodied with anultra-small LED electrode assembly configured to emit blue light,wherein the ultra-small LED electrode assembly may be manufactured byintroducing a solution including ultra-small blue LED devices to amounting electrode line. Further, second subpixels 401 and 501configured to emit red light may be embodied with an ultra-small LEDelectrode assembly configured to emit red light, wherein the ultra-smallLED electrode assembly may be manufactured by introducing a solutionincluding ultra-small red LED devices to another mounting electrodeline. Here, solutions including ultra-small LED devices having differentcolors may be introduced to the mounting electrode lines provided incorresponding subpixels according to a sequence of colors or may besimultaneously introduced to the mounting electrode lines provided inthe corresponding subpixels without the sequence of colors, that is, thepresent invention is not limited to the order of injection andproduction.

In the full-color LED display according to the above-described secondembodiment, the ultra-small LED electrode assembly provided in thesubpixel may have a luminance gain of 1.1 or more according to theabove-described Equation 2, and may preferably have a luminance gain of1.3 or more, which is the same as that of the full-color LED displayaccording to the above-described first embodiment. Further, a percentageof ultra-small LED devices which have the first semiconductor layer indirect or indirect contact with the first mounting electrode among allof the ultra-small LED devices in contact with the mounting electrodemay be 60% or more, and may preferably be 80% or more.

The present invention will be described in detail with the followingexamples, however, the scope of the present invention is not limited tothe following examples, and it should be understood that the followingexamples are intended to assist the understanding of the presentinvention.

Example 1

The electrode lines shown in FIGS. 2A, 3A, and 4A were formed on a basesubstrate formed of a quartz material and having a thickness of 800 μm.Here, in the electrode lines, the first mounting electrode had a widthof 3 μm, the second mounting electrode had a width of 3 μm, a distancebetween the first mounting electrode and the second mounting electrodeadjacent thereto was 2.2 μm, the mounting electrode had a thickness of0.2 μm, materials of the first mounting electrode and the secondmounting electrode were gold, and an area of a region in which theultra-small LED devices were mounted on the mounting electrode line was4.2×10⁷ μm². Then, an insulating layer made of silicon dioxide wasformed in a separate space between lower portions of the mountingelectrode lines on the base substrate. Then, an insulating partitionwall made of silicon dioxide and surrounding the mounting electrode linewas formed, and the insulating partition wall had a height of 0.1 μmfrom an upper portion of the insulating layer to an upper end of theinsulating partition wall.

Subsequently, 0.7 weight % of ultra-small LED devices having a structureshown in Table 1 was mixed with 100 weight % of acetone, and thus asolution including the ultra-small LED devices was prepared.

Then, 9 μl of the solution was dropped onto the electrode line 8 times,and then sine wave power having a voltage of 0 to +30 V and a frequencyof 950 kHz, which is shown in FIG. 15, was applied to the mountingelectrode as assembly power to move and arrange the ultra-small LEDdevices to be self-mounted.

Then, a thermal process was performed to improve a contact of theultra-small LED device and the electrode line. The thermal process wasperformed in a nitrogen atmosphere at a pressure of 5.0×10⁻¹ torr and atemperature of 810° C. for two minutes. Subsequently, an electrolessplating process was performed twice using a 0.05 mM gold aqueoussolution and a copper metal foil at room temperature for 10 minutes.Once again, a thermal process was performed on gold nano particles,which were interposed between the electrode line and the ultra-small LEDdevice using the electroless plating process, under the above conditionsof the thermal process to improve electrical contactability of the goldnano particles so that an LED display including an ultra-small LEDelectrode assembly described in the following Table 2 was manufactured.

TABLE 1 Material Length (μm) Diameter (μm) First electrode Chrome 0.030.5 layer First semi- N-GaN 2.14 0.5 conductor layer Active layer InGaN0.1 0.5 Second semi- P-GaN 0.2 0.5 conductor layer Second Chrome 0.030.5 electrode layer Insulating thin Aluminum Thickness film oxide 0.02Ultra-small — 2.5 0.52 LED device

Examples 2 and 3

Examples 2 and 3 were manufactured using the same method as Examples 1,and LED displays including an ultra-small LED electrode assembly shownin the following Table 2 were manufactured by self-aligning ultra-smallLED devices by applying sine wave powers having voltages and cyclesshown in the following Table 2, which were assembly powers applied tomounting electrodes, to the mounting electrodes.

Comparative Examples 1 to 3

Comparative Examples 1 to 3 were manufactured using the same method asEmbodiment 1, and LED displays including an ultra-small LED electrodeassembly shown in the following Table 2 were manufactured byself-aligning ultra-small LED devices by applying sine wave AC powerhaving a voltage of −30 to +30 V and a frequency of 950 kHz (ComparativeExample 1), sine wave power having a voltage of 0 to +8 V and afrequency of 950 kHz (Comparative Example 2), and sine wave AC powerhaving a voltage of −22 V to +30 V and a frequency of 950 kHz(Comparative Example 3), which were assembly powers applied to mountingelectrodes, to the mounting electrodes.

Experimental Example 1

The following physical properties of one ultra-small LED electrodeassembly provided in each of the LED displays manufactured as Examples 1to 3 and Comparative Examples 1 to 3 were measured, and the results areshown in the following Table 2.

1. Measurement of the Total Number of Ultra-Small LED Devices Mounted inthe Ultra-Small LED Electrode Assembly

A picture of the ultra-small LED electrode assembly was captured usingan optical microscope, and the number of the ultra-small LED deviceshaving both end portions in contact with different two electrodes wascounted.

2. The Number and Percentage of the Ultra-Small LED Devices Mounted tohave a Unidirectional Orientation

The number of the ultra-small LED devices which emitted light due to theultra-small LED electrode assembly being driven with DC power having awaveform of +21.2 V without a cycle was counted to measure the number ofthe mounted ultra-small LED devices having the first semiconductor layerof the ultra-small LED device in contact with the first mountingelectrode among all of the mounted ultra-small LED devices. The countednumber of light emitting ultra-small LED devices was calculated as apercentage based on all of the mounted ultra-small LED devices countedas a result of the first physical property evaluation.

3. Visual Evaluation of Light Emitting Intensity

In order to drive the ultra-small LED electrode assembly, a lightemission picture was captured by applying sine wave AC power having aneffective voltage of 21.2 Vrms and a frequency of 60 Hz to theultra-small LED electrode assembly as a first step, and a light emissionpicture was captured by applying DC power having a waveform of 21.2 Vwithout a cycle to the ultra-small LED electrode assembly as a secondstep. According to the captured results, a light emission picture ofExample 1 in the first step is shown in FIG. 10B, and a light emissionpicture of Example 1 in the second step is shown in FIG. 10C. Further, alight emission picture of Example 2 in the first step is shown in FIG.12A, and a light emission picture of Example 2 in the second step isshown in FIG. 12B. In addition, a light emission picture of ComparativeExample 1 in the first step is shown in FIG. 7B, and a light emissionpicture of Comparative Example 1 in the second step is shown in FIG. 7C.

Specifically, when the light emission pictures are visually inspected,in the case of Examples 1 and 2, degrees of emission in the first step(AC power) and the second step (DC power) were similar, or the degreesof emission in the second step were slightly greater than those in thefirst step. However, in the case of Comparative Example 1, emission inthe first step (AC power) had a much higher degree than that in thesecond step (DC power), and a luminance in the second step (DC power)was visually determined as very low.

4. Measurement of Luminance and Peak Intensity

In order to drive the ultra-small LED electrode assembly, a luminanceand peak intensity thereof were measured using a spectrophotometer byapplying sine wave AC power having an effective voltage of 21.2 Vrms anda frequency of 60 Hz to each of the ultra-small LED electrode assemblyas a first step, and a luminance and peak intensity were measured usingthe spectrophotometer by applying DC power having a waveform of 21.2 Vwithout a cycle to each of the ultra-small LED electrode assembly as asecond step. A value of an area (sum %) in an electric field lightemission spectrum and an intensity proportion (peak %) of light havingmaximum intensity were calculated for each of Examples 1 to 3 andComparative Examples 1 to 3. Here, the value of the area and theintensity proportion in the second step of each of Examples 1 to 3 andComparative Examples 1 to 3 are relatively shown on the basis of thevalue of the area and the intensity proportion in the first stepthereof.

TABLE 2 Example Example Example Comparative Comparative Comparative 1 23 Example 1 Example 2 Example 3 Ultra- Applying 0 V to 0 V to +30 V to−30 V to 0 V to +30 V to small power for 30 V 13 V −10 V +30 V 8 V −22 VLED self-aligning 950 950 950 950 950 950 electrode (assembly kHz kHzkHz kHz kHz kHz assembly power) Asymmetric 30 13 20 0 8 8 assemblyvoltage (V) of Equation 1 Effective 18.4 8.0 17.3 21.2 4.9 18.8 voltage(Vrms, V) of assembly power Total number 88,150 59,011 71.185 166,51720,615 90,891 of mounted ultra-small LED devices Number of 78,910 36,18957,161 81,005 9,615 44,446 unidirectionally oriented ultra-smal LEDdevice Percentage of 89.5 61.3 80.3 48.6 46.6 48.9 unidirectionallyoriented ultra- small LED device (%) First sum % 1.0 1.0 1.0 1.0 1.0 1.0step peak % 1.0 1.0 1.0 1.0 1.0 1.0 (AC power) Second sum % 1.43 1.121.31 0.51 0.81 0.97 step peak % 1.47 1.19 1.34 0.52 0.83 0.99 (DC power)

As shown in Table 2, in the ultra-small LED electrode assembly providedin the LED display according to Comparative Example 1, the intensity ofemitted light based on a total wavelength when DC power was used as thedriving power was merely 0.51 times the intensity of light when AC powerwas used, and the peak intensity (peak %) when the DC power was used wasmerely 0.52 times the peak intensity when AC power was used.

Further, in the case of the ultra-small LED electrode assembly providedin the LED display according to Comparative Example 2 (the asymmetricassembly power according to Equation 1 was 8 V), the intensity ofemitted light based on a total wavelength when DC power was used asdriving power was 0.81 times the intensity of light when AC power wasused and was improved by about 59% of Comparative Example 1, but thenumber of mounted ultra-small LED device was significantly low, and thusa significant decrease of luminance thereof can be predicted.Furthermore, even when the intensity of the emitted light of ComparativeExample 2 based on the total wavelength when the DC power was used asthe driving power was improved from that of Comparative Example 1, theintensity of the light was still significantly low compared to that ofExamples 1 to 3.

Further, in the ultra-small LED electrode assembly provided in the LEDdisplay according to Comparative Example 3, an asymmetric voltage valueaccording to Equation 1 of an applied assembly power was 8 V, which wasidentical to that of Comparative Example 2, but an effective voltage ofthe applied assembly power was 18.8 V, which was significantly increasedfrom a magnitude of that of Comparative Example 2, and thus the numberof mounted devices was significantly increased. However, in ComparativeExample 3, a luminance when DC driving power was used was also lowerthan the luminance when AC driving power was used, and thus the AC powerwas determined to be more suitable as the driving power.

However, in the case of Examples 1 and 2, a luminance when DC power wasused as driving power was much higher than a luminance when AC power wasused as the driving power and, in the case of Example 1, the luminancewhen the DC driving power was used was increased to be 1.43 times theluminance when the AC driving power was used, and the peak intensitywhen the DC driving power was used was increased to be 1.47 times thepeak intensity when the AC driving power was used.

According to the present invention, the amount of photons which aregenerated by ultra-small LED devices, blocked by vertically disposedelectrode lines of a display, and not extracted can be minimize, theultra-small LED device can be connected to ultra-small electrodeswithout defects such as electrical short circuits and the like, and thusthe display can exhibit excellent luminance. Further, since selection ofdriving power of ultra-small LED electrode assemblies has no limit, thedisplay can exhibit a sufficient luminance characteristic using DCdriving power and, in addition, the luminance characteristic can befurther improved by the DC driving power. Furthermore, when a DC drivingvoltage is used, each pixel can exhibit uniform luminance, and thusuniform luminance characteristics and color reproducibility can beexhibited by the entire display. In addition, since intensity of lightcorresponding to a specific wavelength included in an LED itself isfurther improved, when a light color is converted into a light color oflight in a different wavelength to implement full-color, intensity ofthe light having the converted light color is significantly increased,and thus the display can be embodied to have more improved colorreproducibility.

While the present invention has been described with reference toexemplary embodiments thereof, it should be understood that the scope ofthe present invention is not limited to the disclosed exemplaryembodiments, and those skilled in the art should understand that thescope of the present invention may easily suggest other embodimentsthrough the addition, modification, or deletion of components withoutdeparting from the spirit and scope of the present invention.

What is claimed is:
 1. A full-color light emitting diode display havingan improved luminance, comprising a plurality of subpixels, each of theplurality of subpixels comprises at least one ultra-small LED electrodeassembly configured to emit light having substantially the same lightcolor, wherein the ultra-small LED electrode assembly comprises amounting electrode line including a first mounting electrode and asecond mounting electrode, wherein the first mounting electrode and thesecond mounting electrode are formed on the same plane and spaced apartfrom each other; and a plurality of ultra-small LED devices, whereineach of the plurality of ultra-small LED devices have a first end incontact with the first mounting electrode and a second end in contactwith the second mounting electrode; and a luminance gain according toEquation 2 is 1.1 or more: wherein the Equation 2 is shown as below:${{Luminance}\mspace{14mu}{Gain}} = \frac{\begin{matrix}{{Luminance}\mspace{14mu}{of}\mspace{14mu}{ultra}\text{-}{small}\mspace{14mu}{LED}\mspace{14mu}{electrode}} \\{{assembly}\mspace{14mu}{driven}\mspace{14mu}{by}\mspace{14mu}{DC}\mspace{14mu}{voltage}\mspace{14mu}\left( {{cd}\text{/}m^{2}} \right)}\end{matrix}}{\begin{matrix}{{Luminance}\mspace{14mu}{of}\mspace{14mu}{ultra}\text{-}{small}\mspace{14mu}{LED}\mspace{14mu}{electrode}} \\{{assembly}\mspace{14mu}{driven}\mspace{14mu}{by}\mspace{14mu}{AC}\mspace{14mu}{voltage}\mspace{14mu}\left( {{cd}\text{/}m^{2}} \right)}\end{matrix}}$ wherein, a magnitude of an applied direct current voltageV is equal to a magnitude of an effective voltage of sine wavealternating current power.
 2. The full-color light emitting diodedisplay of claim 1, wherein the ultra-small LED electrode assembly has aluminance gain of 1.3 or more according to the Equation
 2. 3. Thefull-color light emitting diode display of claim 1, wherein the lightcolor is blue or white, or the light color is the same as a color of anultraviolet light.
 4. The full-color light emitting diode display ofclaim 1, further comprising an insulating film formed on outer surfacesof the first mounting electrode and the second mounting electrode,wherein the plurality of ultra-small LED devices come into contact withthe first mounting electrode and the second mounting electrode throughthe insulating film.
 5. A full-color light emitting diode display havingan improved luminance, comprising a plurality of subpixels, each of theplurality of subpixels comprises at least one ultra-small LED electrodeassembly configured to emit light having substantially the same lightcolor, wherein the light color is divided into a plurality of differentlight color groups including a first light color, a second light color,and a third light color; the ultra-small LED electrode assemblycomprises: a mounting electrode line including a first mountingelectrode and a second mounting electrode, wherein the first mountingelectrode and the second mounting electrode are formed on the same planeand spaced apart from each other; and a plurality of ultra-small LEDdevices, wherein each of the plurality of ultra-small LED devices has afirst end in contact with the first mounting electrode and a second endin contact with the second mounting electrode; and a luminance gainaccording to Equation 2 is 1.1 or more: wherein the Equation 2 is shownas below: ${{Luminance}\mspace{14mu}{Gain}} = \frac{\begin{matrix}{{Luminance}\mspace{14mu}{of}\mspace{14mu}{ultra}\text{-}{small}\mspace{14mu}{LED}\mspace{14mu}{electrode}} \\{{assembly}\mspace{14mu}{driven}\mspace{14mu}{by}\mspace{14mu}{DC}\mspace{14mu}{voltage}\mspace{14mu}\left( {{cd}\text{/}m^{2}} \right)}\end{matrix}}{\begin{matrix}{{Luminance}\mspace{14mu}{of}\mspace{14mu}{ultra}\text{-}{small}\mspace{14mu}{LED}\mspace{14mu}{electrode}} \\{{assembly}\mspace{14mu}{driven}\mspace{14mu}{by}\mspace{14mu}{AC}\mspace{14mu}{voltage}\mspace{14mu}\left( {{cd}\text{/}m^{2}} \right)}\end{matrix}}$ wherein a magnitude of an applied direct current voltageV is equal to a magnitude of an effective voltage (Vrms) of sine wavealternating current power.
 6. The full-color light emitting diodedisplay of claim 5, wherein among the plurality of light color groups,the first light color is blue, the second light color is green, and thethird light color is red.
 7. The full-color light emitting diode displayof claim 6, wherein the plurality of light color groups furthercomprises a fourth light color group; wherein a light color of thefourth light color group is white.
 8. The full-color light emittingdiode display of claim 5, wherein the ultra-small LED electrode assemblyhas a luminance gain of 1.3 or more according to the Equation
 2. 9. Thefull-color light emitting diode display of claim 5, further comprisingan insulating film formed on outer surfaces of the first mountingelectrode and the second mounting electrode, wherein the plurality ofultra-small LED devices come into contact with the first mountingelectrode and the second mounting electrode through the insulating film.